feat(e2e): add end-to-end tests for kflashback operator

[vak-rashu]

What these tests do:

• Spins up a real KinD cluster with the kflashback controller deployment
• Supports two storage backends via STORAGE_BACKEND env var (sqlite, postgresql)
  • SQLite: deploys controller with PVC-backed storage
  • PostgreSQL: deploys a Postgres instance inside KinD, creates credentials secret, deploys controller
• Creates a "test-app" Deployment in the default namespace
• Updates the deployment twice (image change + replica scaling)
• Verifies changes via the reconstruct API endpoint (/api/v1/resources/{uid}/reconstruct/{revision})
• Asserts reconstructed state matches expected image and replica count at each revision

CI changes:

• Added two parallel e2e jobs (e2e-sqlite, e2e-postgresql) that run on push to main
• Both jobs run after go, docker, integration, manifests and ui jobs pass

Further tests planned:

• spec.paused — verify tracking stops when policy is paused
• spec.retention.maxAge and spec.retention.maxRevisions to verify old revisions are purged correctly

[prashanthjos]

NIT: KinD --> Kind

[vak-rashu]

Updated the workflow naming.